In many applications it is desired to deposit thin layers on a substrate. Known techniques for depositing thin layers are, in particular, evaporating, chemical vapor deposition and sputtering deposition. For example, sputtering can be used to deposit a thin layer such as a thin layer of a metal, e.g. aluminum, or ceramics. During the sputtering process, the coating material is transported from a sputtering target consisting of material to be coated by bombarding the surface of the target with ions of a typically inert processing gas at low pressure. The ions are produced by electron impact ionization of the processing gas and accelerated by a large voltage difference between the target, operating as a sputtering cathode, and an anode. This bombardment of the target results in the ejection of atoms or molecules of the coating material, which accumulate as a deposited film on the substrate arranged opposite to the sputtering cathode, e.g. below the sputtering cathode.
Segmented planar, monolithic planar and rotatable targets may be used for sputtering. Due to the geometry and design of the cathodes, rotatable targets typically have a higher utilization and an increased operation time than planar targets. Accordingly, the use of rotatable targets typically prolongs service life and reduces costs.
A rotary cathode is typically supported by a cathode drive unit of the sputtering installation. During sputtering, the cathode drive unit rotatably transfers movement to the rotary cathode. Given longitudinal extensions of rotary cathodes of, for instance, up to about 4 m and typical continuous operation times of sputtering installations of several days, the bearing of the cathode drive unit is typically desired to reliably support heavy mechanical loads over a long period of time. Sputtering is typically carried out under low pressure or vacuum condition, i.e. in a vacuum chamber. For cost reasons, cathode drive units, in particular when arranged within a vacuum chamber of a sputtering installation, are also desired to consume a small amount of space.
To protect the cathode body from the gas discharge and resultant ion bombardment, dark room shields are provided at both the drive end and the free end of the cathode. They are mounted concentrically to the cathode, maintaining a fixed distance from the cathode surface. The shield around the drive end of the cathode body should prevent the processing gas discharge from contacting the drive end. The dark room shields are mounted on the chamber wall or the drive unit. The shield is electrically isolated from the mounting surface and acquires an electrical potential from the gas discharge.
During sputtering, a film of the depositing material grows onto the surface of the dark room shields, on the area of the dark room shield surface facing the substrate. Eventually, the formed film begins to break into chips or fragments, usually in areas where the film is thicker. If the resulting fragments of material fall onto the substrate, they obstruct deposition on the areas of the substrate which they fall on, resulting in defective products. Therefore, such a dark room shield has to be exchanged often, thus increasing the maintenance costs of the sputtering unit.
Accordingly, there is an ongoing need for an improved device and a method for supporting a rotatable target.